Moody's has slashed Royal Dutch Shell's credit rating, citing the impact of its £36bn acquisition of smaller rival BG on its leverage.
The two companies merged on February 15, creating the world's second-biggest publicly-traded oil and gas company measured by market cap.
But the credit ratings agency warned today that it has left Shell with increased leverage, leading it to downgrade the firm by one notch.
Lower for longer oil prices are also expected to hamper the London-listed firms $30bn (£21.2bn) asset sale program in order to reduce its debt, Moody's said.
"The ratings downgrades and negative outlook reflect Shell's elevated leverage following the BG acquisition," Tom Coleman, Moody's Senior Vice President, said.
"We view BG as a strong contributor to Shell's longer term business positioning, but under a low oil price scenario we expect Shell to generate negative free cash flow at least through 2017."
"Low oil and gas prices will compound Shell's challenges in delivering substantial asset sales to help reduce debt and in integrating and restructuring the upstream portfolio."
Shell is in the midst of a complex integration process that will include thousands of job cuts, tens of billions of pounds in asset sales and the blending of the companies' trading and production operations which overlap in many parts of the world.
It divested $5.5bn worth of assets last year, including a refinery in Japan, North Sea assets and its retail business in Norway.
Moody's also cut Chevron's rating by one level as its on course to generate negative cash flow for at least two years, while Total
Moody's also cut Chevron's rating by one level, while Total's rating was taken down by two pegs.
It said Chevron is likely to struggle with negative cash flow and rising debt levels for two years, while Total's cash flow and credit metrics are expect to come under strain.